[muzani]

Personally, my rule of thumb is that if you don't find something bad about it, you don't know enough about it.

What I do is list down the possible flaws of this idea. Start with the biggest, riskiest flaw and test that. Make the test as simple as possible. If it's a business assumption, you might go up to a potential client and pitch it, see how excited they are about it. Your test is simply a PowerPoint presentation.

At some point, you might need to test cash flow. In that situation you might just want to sell something without a profit, e.g. buy it from the store and sell it, before you get a warehouse full of goods.

Just keep finding small tests. If the tests are too big and expensive, find another idea.